Capacitance on USB Hub Downstream VBUS Line - KBA89330

Question: Is the large capacitor on the downstream VBUS lines really required? It causes a slow drop of the line voltage when the hub is unplugged or unpowered.

Answer:

Yes. The large capacitor is required to provide the required inrush current when a USB device is plugged in. The USB specification requires a minimum 120 µF capacitor on the downstream USB port power lines.